36o SCIENCE PROGRESS 



be shown definitely that ionisation occurs. Haber and Zisch 

 (Z. Physik, 1922, 9, 302) have investigated the ionisation which 

 occurs when oxygen and potassium vapours are mixed. The 

 conductivity at low pressures is considerable, so that there is 

 no doubt that in this case electrically charged particles, possibly 

 electrons, are liberated. By the admixture of sodium vapour 

 with nitrogen, and burning the gaseous mixture in the halogens, 

 he obtained flames with a temperature which was less than 

 that at which temperature radiation becomes visible. At 

 temperatures ranging from 35o°-36o° C. the flame was grey- 

 green in colour, but above this temperature up to 473° C. the 

 normal sodium light was obtained in such an intensity to make 

 it possible to photograph the sodium doublet. From the 

 intensity of the light, it was deduced that the source of the 

 D-line is the free sodium atom, which is activated by collision 

 with a freshly formed molecule, NaCl or NaClg, which has not 

 yet dissipated its energy of combination. Although, in the 

 emission of the D-line by the sodium atom, an electron is 

 transferred only from the normal state to the first quantum 

 orbit, a more violent disturbance may occur, such as that in 

 the mixtures of oxygen and potassium, where the electron is 

 raised to an infinitely large orbit. 



E. B. Andersen (Z. Physik, 1922, 10, 54) has studied the 

 formation of ammonia from mixtures of nitrogen and hydrogen 

 at low pressures under the action of a stream of slow-moving 

 electrons, the variations in electron velocity being secured by 

 variations in the applied electromotive force. No appreciable 

 quantities of ammonia were produced under 18 volts. The 

 maximum rate of formation of ammonia did not correspond 

 with the stoicheiometric mixture of the two gases but in 

 mixtures containing a great excess of nitrogen. This result is 

 in agreement with the view that the first step in the production 

 of ammonia is the ionisation of the nitrogen molecule. The 

 ionisation of the hydrogen molecule is unnecessary. 



Liquid Crystal Formation and Chemical Constitution. — 

 Molecules containing long symmetrical chains of atoms readily 

 give rise to liquid crystals, thus, in aromatic compounds, para- 

 substituted derivatives are especially prone to this form of 

 enantiotropy (D. Vorlander, Zt. Angew Chem., 1922, 15, 

 249). When the symmetry of the molecule is destroyed by 

 the introduction of other groups, either the power of forming 

 liquid crystals is reduced or liquid crystals become the unstable 

 modification. Benzidine derivatives, 



ArCH = N (^—(~y N = CH'Ar, 



give crystals with a wide range of stability, but the 

 introduction of a CH2, CO, CS, S, or O group between the 



